This invention relates to a digital measuring device, and more particularly to a digital measuring device for installation on a machine tool and the like.
Digital measuring devices for displaying a quantity of rotation (the rotational frequency) of a lead screw of the machine tool are disclosed by U.S. Pat. No. 4,117,320 and British Pat. No. 1,499,504. The feed system of the machine tool is generally constructed in such way that a thread is formed on the lead screw and a nut is screwed to the thread of the lead screw and the nut is connected to the cross slide. Another general construction of the feed system of the machine tool is such that the gear is fixed to the lead screw, and the rack is engaged with this gear, and the rack is connected to the cross slide.
In the foregoing construction, when the lead screw is rotated, the cross slide is shifted in the rectilinear direction. Accordingly, when the digital measuring device is mounted on the lead screw, the rotational motion of the lead screw is converted to the pulse signal in an A-D mode, and the pulse signal is counted by a reversible counter, and the quantity of transfer (the transfer distance) of the cross slide is digitally displayed. However, as is well known, the lead screw forming the feed system of the machine tool has a thread accuracy error .DELTA.e and a cumulative lead error .DELTA.E as shown in FIG. 1. Of these errors, the cumulative lead error .DELTA.E can be mechanically corrected, but with respect to the screw accuracy error .DELTA.e, the mechanical correction thereof is not possible. Accordingly, in case the encoder is used for converting the rotational motion of the lead screw to the pulse signal used to count and display the feed quantity of the cross slide by the rotation of the lead screw, there is a drawback in that the error occurs in the display value of the feed quantity of the cross slide by the screw accuracy error .DELTA.e.
Also, in case the feed quantity of the cross slide is counted and displayed by rotating the lead screw connected to the gear, an error similar to the abovenoted error occurs due to the pitch accuracy error of the gear.
Under these circumstances, a primary object of this invention is to display the accurate transfer quantity of the cross slide on the display unit on the basis of the data by utilizing the output pulse on the encoder as the address signal and previously inputting the accurate transfer quantity measuring data corresponding to the address signal to the memory of the microcomputer and then subsequently inputting the output pulses of the encoder to the microcomputer and outputting the data therefrom corresponding to the encoder pulses.
The drawings show the preferred embodiments of this invention. However, it should be noted that various modifications can be made from the constructions disclosed herein, and should not be construed that the drawings and the descriptions specify or limit the scope of this invention .